Untersuchung der Degradation von elektrisch gestresstem nano-porösem ultra low-k Dielektrikum vor dem elektrischen Durchschlag

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Nano-porous ultra low-k dielectrics are important materials for high-speed integrated circuits. They enable low line capacitances, but show poor mechanical properties compared to conventional oxide. This work describes for the first time the intrinsic degradation in nanometer scale after electrical stress stopped before a breakdown occurs. By means of tip type electrode test structures, specifically designed for this investigation and processed in commercially available semiconductor technology, electrical stress and physical analysis have been performed to show degradation patterns. The results show a typical leakage current curve and a formerly unknown dynamic shrinking of the dielectric leading to the development of bubble-shaped holes near the anode. Starting at the anode, tantalum transport into the dielectric has been found. it is assumed, that under operating conditions after some time, shrinking of the dielectric leads to an equilibrium of voids and denser dielectric including fixed oxidized tantalum.